1. Field of the Invention
The present invention relates to a forceps-type medical instrument used during cataract surgery for insertion of an artificial lens in an otherwise natural eye.
2. Prior Art
Moving from the exterior toward the center, a human eye includes the cornea, anterior chamber behind the cornea, iris, posterior chamber behind the iris and vitreous body which encompasses the major portion of the volume of the eyeball. The lens is located in the posterior chamber between the iris and the vitreous and consists of a relatively hard central nucleus surrounded by the softer cortex enclosed in a membrane called the capsule. The capsule and lens structure are held in position centered behind the iris by fibers called zonules that extend between the lens capsule and the periphery of the posterior chamber.
In modern cataract surgery, a short incision is made along the margin of the cornea for access to the lens through the central opening of the iris (pupil). The lens capsule is opened adjacent to the iris and the cloudy natural lens is removed. Preferably, the posterior portion of the lens capsule is left intact so that the posterior chamber remains isolated from the vitreous. Also, the zonules are not disturbed so that the opened lens capsule continues to be supported in the posterior chamber.
In a popular form of cataract surgery, an artificial intraocular lens is implanted after the natural lens has been removed. The intraocular lens includes a clear central optical portion intended to function the same as the clear natural lens of an undamaged and undiseased eye. The intraocular lens is designed to be centered in the posterior chamber. In a common form of intraocular lens, two thin, flexible but slightly resilient filaments called haptics are spiraled tangentially outward from opposite sides of the optical portion of the intraocular lens. The entire artificial lens structure is preferably implanted in the natural lens capsule. The haptics engage against the inner periphery of the capsule and, like weak leaf springs, gently support the optical portion of the artificial lens centered behind the iris.
The implant procedure involves grasping an edge portion of the central optical portion of the artificial lens by lens insertion forceps at a location generally opposite the location where one of the haptics extends. By manipulation of the forceps, such opposite haptic (the inferior haptic) is inserted into the lens capsule through the anterior opening made when the natural lens was removed. The optical portion of the intraocular lens is carefully inserted at least partway into the capsule leaving the trailing haptic (superior haptic) projecting from the capsule. Next, the optical portion of the lens is released and, in accordance with the known procedure, the same forceps are used to grasp the superior haptic and move it past the iris into the posterior chamber. The object is to position the superior haptic such that, when released, it will slowly and gently spring away from the optical portion of the lens and engage inside the lens capsule.
The implant procedure, of course, must be conducted with care because of the delicate nature of the surrounding tissue and the small work space provided by the corneal incision and pupil, but it can be difficult by use of known forceps to position the superior haptic within the natural lens capsule. It is not uncommon for the superior haptic to remain between the jaws of the forceps when released or to deploy outside the capsule, necessitating additional attempts to position the superior haptic properly. Such additional attempts can be irritating to the delicate eye tissue in addition to being frustrating and irritating to the surgeon. There also is the possibility that improper deployment of the superior haptic will not be detected during surgery which can result in the lens decentration and consequently in poor optical performance of the intraocular lens because it is not supported in the lens capsule as intended.